1. Field of the Invention
This invention relates to an improved tape-wound insulation sheath or jacket for an electrical conductor, such as the winding coil or bar of an electrical machine. This insulation sheath is impregnated with a hardenable impregnating resin and afterwards hardened. It is made up of several layers of tape comprising an inorganic, areal or sheet type insulating material, such as mica flakes, mica foils or mica paper, placed upon a flexible or pliable, porous support, which is bonded to said support or to itself or, if necessary, to a cover by a binder.
2. Description of the Prior Art
An example of a tape-wound insulating sheath of the type to which the present invention relates is described in German Pat. DE-PS No. 14 90 427 (to which U.S. Pat. No. 3,458,389 corresponds). Conventional sheaths of this type are wound from only one kind of mica tapes, i.e. mica tapes having one and the same support. To date, primarily porous supports such as paper, fiberglass, or nonwoven material, have been used in order to give a thorough impregnation of the sheath with the impregnating resin mixture.
The thickness of an insulating sheath depends on the permissible operating field strength. In addition, the short-time breakdown strength required by German and other specifications, of more than four times the nominal voltage, must be taken into consideration. In windings of electrical machines, however, a thinner insulation sheath would result in a better slot filling with copper, and the heat resistance between the conductor and the bundle of laminations would be reduced, whereby increased efficiency becomes possible.